Use of monoclonal antibodies to identify, characterize, and purify a 96,000-dalton surface antigen of pathogenic Entamoeba histolytica.

We identified and partially characterized a surface antigen of Entamoeba histolytica by using seven monoclonal antibodies obtained after injecting mice with a pathogenic strain of amoeba. An intrinsically radiolabeled 96,000-dalton antigen was immunoprecipitated by five of the seven monoclonal antibodies; this antigen was present in three strains of E. histolytica. The antigen was situated on the external surface of E. histolytica, as demonstrated by agglutination and immunofluorescence staining of live amoeba and by immunoprecipitation of iodinated trophozoite antigen. All seven monoclonal antibodies were specific for E. histolytica and failed to react in an ELISA with Trichomonas vaginalis, Tritrichomonas foetus, Giardia lamblia, Acanthamoeba castellonii, and Entamoeba invadens. Two monoclonal antibodies were used to purify the antigen: the purified antigen was identical when antibody binding to live organisms or antibody reactive with nonviable organisms was used for purification.